The excited state properties of dibenzothiophene-benzoyl-9,9-dimethyl-9,10-dihydroacridine (DBT-BZ-DMAC) in the solid phase are theoretically studied through a combined quantum mechanics and molecular mechanics (QM/MM) method. The results indicate that the non-radiative decay rate of the molecule in the solid phase is significantly decreased due to the suppression of the rotation of the DMAC and DBT units in the molecule, while the radiative rate is greatly increased owing to the enhancement of the transition dipole moment. Moreover, the fluorescence efficiency in the solid phase (20.5%) is shown to be much larger than that in the gas phase (0.01‰), which confirms that DBT-BZ-DMAC is a typical aggregation-induced emission (AIE) system. The results further display that both the intersystem crossing (ISC) and reverse intersystem crossing (RISC) processes take place between the first singlet excited state (S1) and the lowest degenerate triplet excited states (T1 and T2). In addition, the charge transfer rate is studied using the Marcus theory and the intrinsic charge mobility is calculated by performing the kinetic Monte Carlo method. The results show that the DBT-BZ-DMAC crystal is a p-type semiconductor with a hole mobility of 0.14 cm² V⁻¹ s⁻¹ at room temperature. Our investigation elucidates the experimental measurements and helps one to understand the AIE mechanisms of the DBT-BZ-DMAC fluorescence emitter, which is beneficial for developing new TADF emitters.

Covalent organic frameworks (COFs), featuring semiconductor-like behavior, have recently garnered widespread interest for applications in photocatalysis by virtue of their well-defined and tailorable porous structures, high surface areas and excellent chemical stability. A facile strategy for designing COFs exerting efficient charge transfer and separation as well as suppressing charge carrier recombination is the precise integration of electron-donating and electron-withdrawing moieties to form long-range ordered donor–acceptor (D–A) type structures. In this work, we rationally designed and synthesized a novel imine-linked COF (DABT-Py-COF) by the condensation of a newly designed D–A–D type monomer of 4,4′,4′′,4′′′-(benzo[c][1,2,5]thiadiazole-4,7-diylbis(9,9-dimethyl-9,10-dihydroacridine-10,2,7-triyl))tetrabenzaldehyde and 1,3,6,8-tetrakis(4-aminophenyl)pyrene under solvothermal conditions. Remarkably, the obtained DABT-Py-COF exhibited outstanding and steady hydrogen production with a maximum hydrogen evolution rate (HER) of 5458 μmol g⁻¹ h⁻¹ under visible-light irradiation (AM 1.5). This work has paved the way for the rational design and preparation of more efficient D–A type COFs for photocatalysis.

Through space charge transfer (TSCT)-based thermally activated delayed fluorescence (TADF) molecules with sky-blue emission have drawn great attention in recent studies. Corresponding theoretical investigations to reveal the inner mechanisms are highly desired. Herein, the photophysical properties of a TSCT-based TADF molecule (S-CNDF-S-tCz) are theoretically studied both in solvent and solid environments by using the polarizable continuum model and the combined quantum mechanics and molecular mechanics method, respectively. Based on density functional theory and time-dependent density functional theory coupled with the thermal vibration correlation function method, the adiabatic singlet–triplet energy gap, natural transition orbital properties, TSCT ratio, reorganization energies, intermolecular interactions and rate constants of the intersystem crossing and reverse intersystem crossing processes are analyzed, and the excited state dynamics and energy consumption process are discussed in detail. The results indicate that the geometric changes on the acceptor unit are restricted from chloroform to the solid phase with decreased reorganization energy contributed by the bond angle. Meanwhile, for the remarkable geometric changes on the donor unit from chloroform to the solid phase, the increased reorganization energy is mainly contributed by the bond length and dihedral angle. Moreover, different triplet exciton conversion processes are illustrated for the molecule in chloroform (T₃ → S₁) and the solid phase (T₂ → S₁ and T₂ → S₂ → S₁). In addition, the reduced non-radiative consumption is revealed and a high fluorescence efficiency (29.2%) is achieved in the solid phase, which corresponds well with the experimental results (31%). Furthermore, the distance between the donor and the acceptor is suppressed by intermolecular interactions and an enhanced TSCT feature is observed in the solid phase. Thus, a wise design strategy is confirmed where the TSCT feature can light up a multi-channel reverse intersystem crossing process to increase the triplet exciton utilization for realizing highly efficient TADF emission. Our calculations give a reasonable explanation for the previous experimental measurements and provide a theoretical perspective for the structure–property relationship, which could facilitate the development of new efficient TSCT-based TADF emitters.